Ethyl borate, B

The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). 

Hydrolysis of the ethyl ester proceeded smoothly using hydrochloric acid in acetic acid to give carboxylic acid 69 in 88% yield (Scheme 4.9). Previously, amines were allowed to react with the carboxylic acid core in hot DMSO to deliver the C7 products however, the difluoroborate 70, derived from the carboxylic acid 69, greatly increased the reactivity of the C7 position. Consequently, the displacement of the C7-F with amines was accomplished at lower temperature (Baker et al., 2004 Cecchetti et al., 1996 Domalaga et al., 1993 Ellsworth et al., 2005a,b Hu et al., 2003). In this event, the carboxylic acid was allowed to react with boron trifluoride to deliver difluroboronate 70 in excellent yield. The thus afforded borate ester reacted with A -methylpiperidine in DMSO in the presence of triethylamine at ambient temperature to furnish ( —)-ofloxacin (1, levofloxacin) in 56% yield. 

Dissolve the Potassium Citrate, calcium chloride and sodium borate in approximately 20 ml water. Apply heat if necessary to dissolve. Combine the surfactants, TEA, propylene glycol and ethyl alcohol. Add the Potassium Citrate, calcium chloride and sodium borate solution. Adjust the pH of the solution to B.O with TEA or dilute sodium hydroxide. Add the Protease. 

The paper-chromatographic properties of the common deoxy and dideoxy sugars have been treated in several reviews,2 28 a book,829 and individual publications. Common solvent-systems are 6 4 3 1-butanol-pyridine-water (Solvent A) 4 1 5 1-butanol-acetic acid-water (Solvent B) and 1-buta-nol-ethanol-water (4 1 5, upper phase, Solvent C or 3 1 1, Solvent D). The four 2-deoxy-D-hexoses and the 2,6-dideoxyhexoses may be separated as their borate complexes. 0 The use of 1-butanol-water on the one hand, and of 2-butanone-borate buffer on the other, usually provides adequate separation and, by use of a combination of solvents, these deoxy sugars may be identified. 80 The use of buffered systems has proved highly advantageous in the separation and identification of the isomeric 6-deoxy-hexoses.8 1 Other systems, such as Solvent A and 2 1 2 ethyl acetate-... 

Ebelman and Bouquet prepared the first examples of boric acid esters in 1846 from boron trichloride and alcohols. Literature reviews of this subject are available. B The general class of boric acid esters includes the more common orthoboric acid based trialkoxy- and triaryloxyboranes, B(0R)3 (1), and also the cyclic boroxins, (ROBO)3, which are based on metaboric acid (2). The boranes can be simple trialkoxyboranes, cyclic diol derivatives, or more complex trigonal and tetrahedral derivatives of polyhydric alcohols. Nomenclature is confusing in boric acid ester chemistry. Many trialkoxy- and triaryloxyboranes such as methyl, ethyl, and phenyl are commonly referred to simply as methyl, ethyl, and phenyl borates. The lUPAC boron nomenclature committee has recommended the use of trialkoxy- and triaryloxyboranes for these compounds, but they are referred to in the literature as boric acid esters, trialkoxy and triaryloxy borates, trialkyl and triaryl borates or orthoborates, and boron alkoxides and aryloxides. The lUPAC nomenclature will be used in this review except for relatively common compounds such as methyl borate. Boroxins are also referred to as metaborates and more commonly as boroxines. Boroxin is preferred by the lUPAC nomenclature committee and will be used in this review. 

A small-scale procedure, based on the reaction of bis(trifluoroethyl) alkylboronates with diphenylprolinol (eq 7) was reported for the preparation of the B-ethyl- (9b) and B-butyl-(9c) oxazaborolidines. The bis(trifluoroethyl) alkylboronates were prepared from the disproportionation of tris(trifluoroethyl) borate and the corresponding trialkylborane. Since trimethylb-orane is not commercially available, this procedure is not applicable for the preparation of B-methyloxazaborolidine (9a). 

The B chemical shifts of the 6-phenyl-, 6-phenyl-l,2-dimethyl-and the 6-ethyl-derivatives of (3)-l,2-dicarbadodecahydroundeca-borate(-l) were generally uninformative the singlet boron signal from the B-phenyl or B-ethyl group could not even be distinguished. 

A variety of chelates of B-compounds are formed by polyols. For instance, phenyl glycol may be used to extract sodium borate from dilute aqueous solutions. Recently, 2-ethyl-hexanol in kerosene was used to extract boric acid from aqueous solutions (57). 

Figure 5.13 Separation of phenolic antioxidants by thin-layer chromatography. Solvent benzene development distance 15 cm indicators (a) borate buffer (b) 0.1% 2,6-dichloro quinonechlorimide in methanol. 1 = hydroquinone monobenzyl ether 2 = 2,6-di-rerr-butyl-phenol 3 = 2,6-di-tert-butyl-4-methyl-phenol 4 = 2,6-di-tcrt-butyl-a-methoxy-4-methyl-phenol 5 = 2-a-methyl-cyclohexyl-4, 6-dimethyl-phenol 6 = butylated hydroxyanisole 7 = butylated hydroxy toluene 8 = 4,4"-bis (2,6-di-terf-butyl-phenol) 9 = 2,2"-methylene-bis (4-methyl-6-terf-butyl-phenol) 10 = 2,2"-methylene-bis (4-ethyl-6-fert-butyl-phenol) Reproduced from Kreiner and Warner, Journal of Chromatography [119]...

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